r/SpaceX Discusses [May 2018, #44]

You have correctly pointed out the major issue which is that SpaceX would need to find seven missions that are low enough performance that they could avoid the use of sub-cooled propellants. Not only would the propellant mass decrease but the effect would be uneven as the LOX is more highly densified (10%) than the RP-1 (3%) so either the mixture ratio would need to be changed or the RP-1 tank would need to be partially filled.

It is likely that the Block 5 engines will not run at full thrust with warm propellant due to cavitation at the LOX turbopump inlet and more helium COPVs will likely be required as the helium will be warmer.

Essentially there will then be two closely related but different vehicles flying as F9 which will make everything more difficult for SpaceX and will certainly tend to decrease the reliability of the "crew rated" booster.

/r/spacex Thread Parent